In terms of #3, anywhere developers can build residential, they will. Rents & prices on residential are much higher. Unfortunately Manhattan zoning prevents residential in large parts of the city. I believe that is why there are so many hotels going up in the 20s/30s on the west side, when that is someday rezoned it will be easier to convert to residential than offices would have been.
The garment district (the 20s/30s on the West Side) is zoned industrial. Hotels are legal in industrial zones, but apartments aren't, so hotels get built.
